Legal Definitions - reasonable-use theory

The reasonable-use theory is a legal principle that governs the rights of landowners who own property adjacent to a natural body of water, such as a river, stream, or lake. These landowners are often referred to as "riparian owners."

Under this theory, a riparian owner has the right to make a reasonable use of the water that flows past or through their land. However, this right is not absolute. The crucial condition is that their use must not significantly diminish the quantity or quality of water available to other riparian owners located downstream or along the same body of water. The goal is to balance the needs and interests of all landowners who share access to a common water source, ensuring that one owner's actions do not unfairly deprive others of their water rights.

Here are some examples illustrating the reasonable-use theory:

• Residential Garden Irrigation: Imagine a homeowner whose property borders a small creek. During a dry summer, they use a small pump to draw water from the creek to irrigate their backyard vegetable garden. This would generally be considered a reasonable use because watering a modest garden is a common domestic activity, and the amount of water taken is typically small enough not to significantly reduce the creek's flow for their neighbors living downstream. If, however, they diverted the entire creek to fill a large private swimming pond, leaving no water for downstream properties, that would likely be deemed an unreasonable use.

• Small Farm Livestock Watering: Consider a small family farm located next to a river. The farmer allows their livestock, such as a small herd of cattle, to drink directly from the river. This is generally a reasonable use as it's essential for the animals' survival and a typical agricultural practice. The amount of water consumed by a small herd would not typically impact the river's flow or quality for other farmers or residents further downriver. An unreasonable use might involve building a large commercial feedlot that requires massive amounts of water diversion and generates significant pollution, making the water unusable for downstream users.

• Recreational Boating and Docking: A property owner on a large lake builds a private dock and uses the lake for recreational activities like swimming, fishing, and boating. These are generally considered reasonable uses of the water. The presence of a dock and the occasional use of the lake for recreation do not typically diminish the water available to other lakefront owners or those accessing the lake. An unreasonable use, however, might involve constructing a massive structure that obstructs navigation, significantly alters the shoreline, or pollutes the lake in a way that harms other users or the environment.